Apologies if this is mentioned in the post as I didn't see it...

I would add this one:

If you're adding more than one plugin, especially one you've never used before, only add one at a time. Then test to make sure it's behaving with your site, theme, and other plugins.

If you add several at once and have a problem, you won't know which one is the culprit.

Don't ask me how I know about this... ;)

Bob